2. When reference points are available in the foreground, distant objects appear bigger. If you see the moon rising through the trees, the moon will appear immense, because your brain is unconsciously comparing the size of the object in the foreground (the tree limbs) with the moon in the background. When you see the moon up in the sky, it is set against tiny stars in the background.
Artists often play with distorting perception by moving peripheral objects closer to the foreground. Peter Boyce, of the American Astronomical Society, adds that reference points tend to distort perception most when they are close to us and when the size of the reference points is well known to the observer. We know how large a tree limb is, but our mind plays tricks on us when we try to determine the size of heavenly objects. Loudon states that eleven full moons would fit between the pointer stars of the Big Dipper, a fact we could never determine with our naked eyes alone.
3. The moon illusion may be partially explained by the refraction of our atmosphere magnifying the image. But even the astronomers who mentioned the refraction theory indicated that it could explain only some of the distortion.
A few skeptics, no doubt the same folks who insist that the world is flat and that no astronaut has ever really landed on the Moon, believe that the Moon really is larger at the horizon than when up in the sky. If you want to squelch these skeptics, here are a few counterarguments that the astronomers suggested.
1. Take photos of the Moon or Sun at the horizon and up in the sky. The bodies will appear to be the same size.
2. “Cover” the Moon with a fingertip. Unless your nails grow at an alarming rate, you should be able to cover the Moon just as easily whether it is high or low.
3. Best of all, if you want proof of how easy it is to skew your perception of size, bend over and look at the Moon upside down through your legs. When we are faced with a new vantage point, all reference points and size comparisons are upset, and we realize how much we rely upon experience, rather than our sensory organs, to judge distances and size.
We do, however, suggest that this physically challenging and potentially embarrassing scientific procedure be done in wide-open spaces and with the supervision of a parent or guardian. Imponderables cannot be held responsible for the physical or emotional well-being of those in search of astronomical truths.
Submitted by Patrick Chambers, of Grandview, Missouri.
* * *
WHEN YOU ARE DRIVING YOUR CAR AT NIGHT
AND LOOK UP AT THE SKY, WHY DOES IT SEEM
THAT THE MOON IS FOLLOWING YOU AROUND?
* * *
If you, like every other literate human being, have read the previous entry, then you know why the Moon looks larger on the horizon than up in the sky, even though the Moon remains the same size. Clearly, our eyes can play tricks on us.
Without reference points to guide us, the Moon doesn’t seem to be far away. When you are driving on a highway, the objects closest to your car go whirring by. Barriers dividing the lanes become a blur. You can discern individual houses or trees by the side of the road, but, depending upon your speed, it might be painful to watch them go by. Distant trees and houses move by much more slowly, even though you are driving at the same speed. And distant mountains seem mammoth and motionless. Eventually, as you travel far enough down the highway, you will pass the mountains, and they will appear smaller.
If you think the mountain range off the highway is large or far away, consider the Moon, which is 240,000 miles away and bigger than any mountain range (more than 2,100 miles in diameter). We already know that our eyes are playing tricks with our perception of how big and far away the Moon is. You would have to be traveling awfully far to make the Moon appear to move at all. Astronomy editor Jeff Kanipe concludes that without a highway or expanse of landscape to give us reference points “this illusion of nearness coupled with its actual size and distance makes the Moon appear to follow us wherever we go.”
This phenomenon, much discussed in physics and astronomy textbooks, is called the parallax and is used to determine how the apparent change in the position of an object or heavenly body may be influenced by the changing position of the observer. Astronomers can determine the distance between a body in space and the observer by measuring the magnitude of the parallax effect.
And then again, Elizabeth, maybe the Moon really is following you.
Submitted by Elizabeth Bogart of Glenview, Illinois.
* * *
WHY IS SEAWATER BLUE AND TAP WATER
CLEAR? WHY DOES THE COLOR OF THE
OCEAN RANGE FROM BLUE TO RED?
* * *
White light consists of all the primary and secondary colors in the spectrum. Each color is distinguished by the degree to which it scatters and absorbs light. When sunlight hits seawater, part of it is absorbed while the rest is scattered in all directions after colliding with water molecules.
When sunlight hits clear water, red and infrared light absorb rapidly, and blue the least easily. According to Curtiss O. Davis of the California Institute of Technology’s Jet Propulsion Laboratory, “only blue-green light can be transmitted into, scattered, and then transmitted back out of the water without being absorbed.” By the time the light has reached ten fathoms deep, most of the red has been absorbed.
Why doesn’t tap water appear blue? Curtiss continues: “To see this blue effect, the water must be on the order of ten feet deep or deeper. In a glass there is not enough water to absorb much light, not even the red; consequently, the water appears clear.”
Thus if clear water is of a depth of more than ten feet, it is likely to appear blue in the sunlight. So how can we explain green and red oceans?
Both are the result not of the optical qualities of sunlight but of the presence of assorted gook in the water itself. A green sea is a combination of the natural blue color with yellow substances in the ocean—humic acids, suspended debris, and living organisms. Red water (usually in coastal areas) is created by an abundance of algae or plankton near the surface of the water. In open waters, comparatively free from debris and the environmental effect of humans, the ocean usually appears to be blue.
Submitted by Jim Albert, of Cary, North Carolina.
* * *
HOW CAN THE RELATIVE HUMIDITY BE
UNDER 100 PERCENT WHEN IT IS RAINING?
* * *
Air moves in layers. Often, rain occurs when a higher warm, moist air mass overwhelms a cool, dry air mass at ground level.
Humidity is measured at ground level. When the rain from the higher layer falls through the dry air layer, the humidity on the surface rises, but need not rise to 100 percent. Conversely, when the moist layer is below the high pressure system, the humidity can reach 100 percent on the surface even if the upper air layer is dry.
* * *
WHY DOES THE DIFFERENCE BETWEEN
75 DEGREES AND 80 DEGREES IN WATER
TEMPERATURE FEEL QUITE SEVERE WHEN
A FIVE-DEGREE DIFFERENCE IN THE
AMBIENT AIR BARELY REGISTERS?
* * *
The conductivity of water is much higher than air. If the water in a swimming pool is colder than body temperature, the water will conduct heat quickly away from our bodies. If it is warmer, such as in a hot tub, the water just as rapidly transfers heat to the body. Differences in temperature in the ambient air transfer heat in the same directions but at a much slower rate.
Richard A. Anthes, president of the University Corporation for Atmospheric Research, emphasized to Imponderables: “It is the rate of conduction of heat that we sense as heat or cold.”
Submitted by Glenn Worthman of Palo Alto, California.
* * *
WHAT IS THE OFFICIAL NAME OF THE MOON?
* * *
A long with our correspondent, we’ve never known what to call our planet’s satellite. Moon? The moon? moon? the moon? Dorothy?
We know that other planets have moons. Do they all have names? How do astronomers distinguish one moon from ano
ther?
Whenever we have a problem with matters astronomical, we beg our friends at two terrific magazines—Astronomy and Sky & Telescope—for help. As usual, they took pity on us.
Astronomy’s Robert Burnham, like most senior editors, is picky about word usage:
The proper name of our sole natural satellite is “the Moon” and therefore…it should be capitalized. The 60-odd natural satellites of the other planets, however, are called “moons” (in lower case) because each has been given a proper name, such as Deimos, Amalthea, Hyperion, Miranda, Larissa, or Charon.
Likewise, the proper name for our star is “the Sun” and that for our planet is “Earth” or “the Earth.” It’s OK, however, to use “earth” in the lower case whenever you use it as a synonym for “dirt” or “ground.”
Alan MacRobert, of Sky & Telescope, adds that Luna, the Moon’s Latin name, is sometimes used in poetry and science fiction, but has never caught on among scientists or the lay public: “Names are used to distinguish things from each other. Since we have only one moon, there’s nothing it needs to be distinguished from.”
Submitted by A. P. Bahlkow of Sudbury, Massachusetts.
* * *
WHAT IN THE HECK IS A TUMBLEWEED?
WHY DOES IT TUMBLE? AND HOW CAN IT
REPRODUCE IF IT DOESN’T STAY
IN ONE PLACE?
* * *
Three Imponderables for the price of one. The first part is easy. The most common form of tumbleweed, the one you see wreaking havoc in movie westerns, is the Russian thistle. But actually the term is applied to any plant that rolls with the wind, drops its seed as it tumbles, and possesses panicles (branched flower clusters) that break off.
Usually, the stems of tumbleweed dry up and snap away from their roots in late fall, when the seeds are ripe and the leaves dying. Although tumbleweeds cannot walk or fly on their own, they are configured to move with the wind. The aboveground portion of the thistle is shaped like a flattened globe, so it can roll more easily than other plants.
In his March 1991 Scientific American article “Tumbleweed,” James Young points out how tumbleweed has adapted to the arid conditions of the Great Plains. One Russian thistle plant can contain a quarter of a million seeds. Even these impressive amounts of seeds will not reproduce efficiently if dumped all at once. But the flowers, which bloom in the summer, are wedged in the axil between the leaves and the stem, so that their seeds don’t fall out as soon as they are subjected to their first tumbles. In effect, the seeds are dispersed sparingly by the natural equivalent of time-release capsules, assuring wide dissemination.
Young points out that tumbleweed actually thrives on solitude. If tumbleweed bumps into another plant, or thick, tall grass, it becomes lodged there, and birds and small animals find and eat the seeds:
Hence, successful germination, establishment of seedlings, and flowering depend on dispersal to sites where competition is minimal: Russian thistle would rather tumble than fight.
Although songs have romanticized the tumbleweed, do not forget that the last word in “tumbleweed” is “weed.” In fact, if the Russian thistle had been discovered in our country in the 1950s rather than in the 1870s, it probably would have been branded a communist plot. Thistle was a major problem for the cowboys and farmers who first encountered it. Although tumbleweed looks “bushy,” its leaves are spiny and extremely sharp. Horses were often lacerated by running into tumbleweed in fields and pastures, and the leaves punctured the gloves and pants worn by cowboys.
Tumbleweed has also been a bane to farmers, which explains how tumbleweed spread so fast from the Dakotas down to the Southwest. The seeds of tumbleweed are about the same size as most cereal grains. Farmers had no easy way to separate the thistle seeds from their grains; as “grain” moved through the marketplace, thistle was transported to new “tumbling ground.”
Today, tumbleweed’s favorite victims are automobiles and the passengers in them. We get into accidents trying to avoid it, trying to outrace it, and from stupid driving mistakes when simply trying to watch tumbleweed tumble.
Submitted by Plácido García of Albuquerque, New Mexico.
* * *
WHY DO OTHER PEOPLE HEAR OUR VOICES
DIFFERENTLY THAN WE DO?
* * *
We have probably all had this experience. We listen to a tape recording of ourselves talking with some friends. We insist that the tape doesn’t sound at all like our voice, but everyone else’s sounds reasonably accurate. “Au contraire,” the friend retorts. “Yours sounds right, but I don’t sound like that.” According to speech therapist Dr. Mike D’Asaro, there is a universal pattern of rejection of one’s own voice. Is there a medical explanation?
Yes. Speech begins at the larynx, where the vibration emanates. Part of the vibration is conducted through the air—this is what your friends (and the tape recorder) hear when you speak. Another part of the vibration is directed through the fluids and solids of the head. Our inner and middle ears are parts of caverns hollowed out by bone—the hardest bone of the skull. The inner ear contains fluid; the middle ear contains air; and the two are constantly pressing against each other. The larynx is also surrounded by soft tissue full of liquid. Sound transmits differently through the air than through solids and liquids, and this difference accounts for almost all of the tonal differences we hear when reacting negatively to our own voice on a tape recorder.
When we listen to our own voice while we speak, we are not hearing solely with our ears, but also through internal hearing, a mostly liquid transmission through a series of bodily organs. During an electric guitar solo, who hears the “real” sound? The audience, listening to amplified, distorted sound? The guitarist, hearing a combination of the distortion and the predistorted sound? Or would a tape recorder located inside the guitar itself hear the “real” music? The question is moot. There are three different sounds being made by the guitarist at any one time, and the principle is the same for the human voice. We can’t say that either the tape recorder or the speaker hears the “right” voice, only that the voices are indeed different.
Dr. D’Asaro points out that we have an internal memory of our voice in our brain, and the memory is invariably richer than what we hear in a tape recorder playback. Although there seems to be no consistent pattern in whether folks hear their voices as lower or higher pitched than other listeners, there is no doubt that internal hearing is of much higher fidelity than external hearing. Listening to our own voice on a tape recorder is like listening to a favorite symphony on a bad transistor radio—the sound is recognizable but a pale imitation of the real thing.
* * *
IF YOU DIG A HOLE AND TRY TO PLUG
THE HOLE WITH THE VERY DIRT YOU’VE
REMOVED, WHY DO YOU NEVER HAVE
ENOUGH DIRT TO REFILL THE HOLE?
* * *
After speaking to several agronomists, we can say one thing with certainty: Don’t use the word “dirt” casually among soil experts. As Dr. Lee P. Grant of the University of Maryland’s Agricultural Engineering Department remonstrated with us, dirt is what one gets on one’s clothes or sweeps off the floor. Francis D. Hole, professor emeritus of soil science and geography at the University of Wisconsin-Madison, was a little less gentle:
What would you do if you were some fine, life-giving soil who is twenty thousand years the senior of the digger, and you were operated on by this fugitive human being with a blunt surgical instrument (but without a soil surgeon’s license), and if you were addressed as so much “dirt,” to boot? I am suggesting that a self-respecting soil would flee the spot and not be all there for you to manipulate back into the hole.
So there’s the answer: The soil is offended by you calling it dirt, Loren, and has flown the scene of your crime against it.
We promised Grant and Hole we would treat soil with all the respect it was due, and temporarily suppress the use of the “d” word, if they would answer our question. They provided several explanations f
or why you might run out of soil when refilling a hole:
1. Not saving all the soil. Dr. Hole reported one instance, where in their excitement about their work, a team of soil scientists forgot to lay down the traditional canvas to collect the collected soil: “We had lost a lot of the soil in the forest floor, among dead branches and leaves.”
2. You changed the soil structure when you dug up the dirt. Grant explains:
Soil is composed of organic and inorganic material as well as air spaces and microorganisms. Soil has a structure which includes, among other things, pores (or air spaces) through which water and plant roots pass. Within the soil are worm, mole, and other tunnels and/or air spaces. All of this structure is destroyed during the digging process.
Hole confirms that stomping on the hole you are refilling can also compact the soil, removing pores and openings, resulting in plugging the hole too tight:
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